bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Pip Cet]

On Fri, May 29, 2020 at 10:16 AM Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Fri, 22 May 2020 10:22:56 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 41321@debbugs.gnu.org
> >
> > > > I'm already running with such a breakpoint, let's how it will catch
> > > > something.                                        ^^^
> > >
> > > Should have been "hope".  Sorry.
> >
> > It happened again, and now insert-file-contents wasn't involved, so I
> > guess it's off the hook.  The command which triggered the problem was
> > self-insert-command, as shown in the backtrace below.  The problem
> > seems to be with handling overlays when buffer text changes.
>
> One more segfault very similar to the last one I reported: it happened
> when calling report_overlay_modification due to text being inserted
> into a buffer.

Everything looks consistent with the bug I described.

> . There's nothing wrong with GDB's xtype command: it fails when a Lisp
>   object encodes a pointer to invalid memory:

(gdb) p last_marked[497]
$100 = XIL(0x439c370)
(gdb) xtype
Lisp_Vectorlike
Cannot access memory at address 0x1ffac2a8

Again, that can't be right. $100 is a Lisp_Symbol, not a vectorlike,
and it's not at address 0x1ffac2a8.

So my suspicion remains that this is a gdb bug, and it appears to be a
reproducible one!

> . So we should
>   see whether fixing the LISP_ALIGNMENT vs GCALIGNMENT discrepancy
>   fixes this problem.

I concur.